WASHINGTON — When Eric Garner died in a police chokehold in Staten Island, N.Y. — an episode that helped spawn a national protest movement and the rallying cry “I can’t breathe!’’ — Erica Garner lost her father and Gwen Carr lost her son.

But while granddaughter and grandmother are united in their grief and anger over violent police behavior, they are divided in the political battle between Bernie Sanders and Hillary Clinton for the trust and support of black voters.

Erica Garner, 25, is backing Sanders and describes the impact of her father’s 2014 death on her family in a new Sanders campaign video.

Gwen Carr, 66, publicly supports Clinton, writing recently on behalf of the campaign that Clinton “seems to be the only candidate right now who’s talking about how we can be strategic’’ in fighting police brutality.

Both women have committed to campaign in the crucial primary state of South Carolina on their respective behalf — Garner this past weekend, Carr later this month. The Democratic primary is Feb. 27.

The family split illuminates the generational differences at work in the Democratic nominating contest, a chasm that Sanders hopes to widen in states with high concentrations of African-American voters. Will Clinton be able to count on continued black support as the primary heads to more diverse southern states? Or will Sanders peel off young black voters just as he resoundingly won the youth vote in Iowa and New Hampshire?

The answers to these questions will determine whether Sanders is able to take his calls for a liberal political revolution deeper into the contest, or if his fortunes will fade in the next month.

Clinton and Sanders both called for police and criminal justice reform in last week’s debate in Wisconsin. They dueled over the strength of their support for President Obama, the first black president. And they made thinly veiled appeals for African-American support.

A new Reuters poll shows that young African-Americans are more open than their parents or grandparents to supporting Sanders. Clinton has a 45-point lead on Sanders among black voters nationally, but among those 18 to 29 years old, the margin shrinks to 46 percent for Clinton and 33 percent for Sanders.

“I wish there were a black Democrat standing up for us out there, but Bernie is the closest thing to that. I can relate to him,’’ Erica Garner said in an interview with the Globe. She said she has not spoken to her grandmother about their difference of opinion about the Democratic candidates.

Eric Garner, a 43-year-old father of six, was placed in a banned chokehold by police as he was arrested outside a Staten Island strip mall for selling cigarettes. The medical examiner ruled his death a homicide but a grand jury did not indict the officer who placed Garner in the chokehold; the US Department of Justice is conducting a separate investigation.

The arrest was caught by a bystander on his cellphone camera and broadcast around the world. It added to the protest movement over a wave of recordings of violent police confrontations with unarmed African-Americans.

Hours before the Thursday debate, the Sanders campaign released an emotional four-minute video online featuring Eric Garner’s eldest daughter and her 6-year-old daughter in their Williamsburg neighborhood in Brooklyn. Sanders, the son of working-class Polish immigrants, also grew up in Brooklyn.

In the video, Garner speaks candidly about discussing the civil rights movement and her activism with her daughter, Alyssa, in honor of her “pop pop,’’ whom she saw die on national television in July 2014.

Sanders’ name is not mentioned until two and a half minutes into the video, which then cuts between snippets of Sanders’ speeches on race and police brutality and images of Erica Garner and her family.

“I’m behind anyone who is going to listen and speak up for us, and I think we need to believe in a leader like Bernie Sanders,’’ Erica Garner said in the video. “I believe Bernie Sanders is a protester.’’

Garner, who worked as a Dunkin’ Donuts cashier before becoming a full-time activist, told the Globe that she first reached out to Sanders’ campaign two months ago after learning about Sanders fighting to end institutional segregation while he was an undergraduate at the University of Chicago. She officially announced her endorsement via an op-ed piece in The Washington Post in January.

The endorsement would have seemed unthinkable just six months ago, when Black Lives Matter protesters interrupted one of his speeches and he threatened to leave.

Sure, the “optics were messy’’ last summer, Garner wrote in the Post, but Sanders has since “prioritized a racial justice platform’’ and “declared that black lives do matter.’’

Tad Devine, a Democratic media consultant working for Sanders, said he got the idea for the Garner ad after reading her piece in the Post, using her own words as the script. The campaign has so far been unable to secure a 4-minute broadcast slot, so Devine said it plans to cut the video in half and run the ad on national cable channels MSNBC, CNN, and BET.

“We just have to figure out how to keep the movement alive and not get in the way of it,’’ Devine said. “Our whole sort of challenge here has been to get the advantage in age and try to push that as high as we can go. That division is not inhibited by race.’’

Gwen Carr did not respond to Globe requests for an interview. Like her granddaughter, she became a full-time activist following her son’s death and retired from her job as a New York subway train operator. She appears every Saturday at rallies held by the Rev. Al Sharpton in Harlem.

Carr put out a statement last month when she endorsed Clinton, saying, “Along with too many others, Eric’s death has forced our country to confront the effects of police brutality. We’ve got to do something about the violence in our communities — especially gun violence — and the racial and economic injustice that’s connected to it.’’

Carr and other African-American mothers will be traveling to Charleston, S.C., later this month to highlight Clinton’s record on gun reform, according to the Clinton campaign.

Both Clinton and Sanders have outlined extensive plans for criminal justice reform. Clinton has said she wants to reform mandatory minimum sentences, end private prisons, encourage the use of police body cameras, and support legislation to end racial profiling by law enforcement.

Sanders is calling for broader racial justice reform to end the “violence waged against black, brown and indigenous Americans,’’ according to his website. It includes demilitarizing the police, better training and data collection, and increasing civilian oversight of police departments. He also supports ending private prisons and requiring police body cameras.

As for reaching the South Carolina electorate, where African-Americans make up nearly 60 percent of Democratic primary voters, Sanders’ new ad featuring Erica Garner could very well help the 74-year-old democratic socialist win over black voters, who overwhelmingly support Clinton.

“It’s a powerful ad. He will probably make headway. Senator Sanders is resonating with young voters, African-American and white,’’ said Jaime Harrison, the first African-American to chair the South Carolina Democratic Party and who remains unaligned.

But while young voters were an important part of the Obama coalition that gave him the winning edge in 2008 and 2012, the most reliable voters in the South Carolina Democratic primary remain middle-aged African-American women, according to polls and Harrison.

“They are the ones who vote right now, and people are trying to make up their minds on who is best equipped to carry the water for them and their families,’’ Harrison said.

Tracy Jan can be reached at tracy.jan@globe.com. Follow her on Twitter @TracyJan.